1. Field of Invention
The invention herein relates to sails, specifically wing sails for wind powered craft.
2. Description of Prior Art
Designers and manufacturers of wind powered craft, supply consumers with a number of custom sails for a specific sailing craft. Sail designers and sail makers provide the most efficient designs possible for the current technology. Racing and cruising sailors are the impetus for product development, toward more power, simplicity of use, and safety.
Sails with the most power are not easy to use, and are not safe to use with possible high winds. The most common sails are not easy to use, and suffer a loss of efficient use of the winds power of up to thirty seven percent. Even in the hands of professionals, sail trim requires a lot of attention, and handling to keep the power of the wind working for the craft.
For wind powered craft, it has been a long held claim, that the solid wing with flaps and headsail twist, is the one hundred percent efficient use of the winds power. An example is Wainwrights; Aerofoil Sail, U.S. Pat. No. 4,402,277 in 1983. However, solid wings come short of this claim. For airfoil shape control, solid wings have huge flaps. These wings require a substantial amount of adjustment. An airfoils efficiency is in direct proportion to its"" draft to chord ratio, which must change with increased, or decreased wind speeds automatically. Solid wings are not flexible enough to change draft, or flatten the windward panel automatically. Rigid wings have a substantial reduction of useful efficiency, as they cannot be stowed, and the whole wing must be hauled out for possible high wind speeds. Additional sails are required for all useable wind conditions, and the craft cannot stow away a spare wing.
Semi rigid wings made of battened sailcloth answer the need for stowing a wing, however, the wind applied to the soft surface buckles the sailcloth back inside of the wing and jams the folding process. Additionally, to be efficient, a wing has to have a more rigid leading edge, of which sailcloth with battens does not provide. For example, reference Magrini""s, Wing Sail Structure, U.S. Pat. No. 5,271,349 in 1993, and Elmali""s reversible camber line flexible wing sail, U.S. Pat. No. 4,895,091 in 1990. Another soft wing sail variation is Ljundstrom""s Rig, U.S. Pat. No. 2,107,303 in 1938. A boom-less, batten-less, soft twin sail that stows wound up around a rotating mast, and can be spread apart for following winds. On the wind, the mast forms the leading edge inside the twin sails. When reefed, the rolled up dual panels become the same as a standard single sail panel, which is an inefficient airfoil shape.
Lapwing Rig, by H. G. Hasler, around 1960, reference; Singlehanded Sailing 2nd Edition, page 128, by Richard Henderson, 1988 International Marine Publishing Company. A xe2x80x9cModified Ljundstrom rigxe2x80x9d, added twin booms. For following winds, the clew of the twin booms can be separated, allowing the sail panels to wing out, and form a following wind sail. The boom is an improvement, but the airfoil remains as inefficient as standard soft sails.
Gallant Rig, by Jack Manners Spencer, of England, reference; Singlehanded Sailing 2nd Edition, page 128, by Richard Henderson, 1988, International Marine Publishing Company. A fully battened soft twin sail, enveloping the mast. Stows horizontally. This sail is also soft, and inefficient. The battens make it difficult to adjust the airfoil shape from head to foot.
Compromises between solid wing, and standard sail have been made, in efforts to improve efficiency and safety for everyday use. An example is the xe2x80x9cLady Helmsmanxe2x80x9d by Austin Farrar in 1965, reference; Faster The Quest For Sailing Speed, page 56, by David Pelly, 1984, Hearst Marine Books. The rotating partial solid wing mast, with a fully battened mainsail improves efficiency over that of standard sails. However, safety for the craft is compromised by storm winds, and by the increased weight affecting the righting moment. Also, as with standard sails, the airfoil shape is not automatic, and is complex to adjust. Additional sails are required for all useable wind conditions.
N.A.C.A. 653-418 wing section, by John H. Quinn Jr., 1944, wing section with boundary layer control by suction through a span wise slot at the point of separated flow in the leeward surface. Reference; Theory Of Wing Sections, page 236, by Abbott and Doenhoff, 1959, Dover Publications. A mechanical pump provides suction. The solid wing section as described is a one direction lifting airfoil. Intended for, and suitable only for xe2x80x9cheavy displacement aircraftxe2x80x9d.
Airfoils of single panel sailcloth suffer a substantial loss of efficient use of the winds power. Which can be as much as a 17 to 37% loss of efficiency, when compared to wing sails. Rating reference; The Cruising Catamaran Advantage, page 165, by Rod Gibbons, 1988, Island Educational Publishing. Many changes of sails are required for different wind conditions. Also they require constant adjusting to control their airfoil shape. With a shaped mast there is only a slight increase in efficiency. This efficiency is increased slightly more with the masts ability to rotate its leading edge toward the wind. Standard sails are the most widely used, whether for working, sport, or pleasure craft. These sails are inefficient, and are not safe to use, because they are not easy to change. Rapidly degrading weather can ruin the sails, and inflict serious injury to persons handling them. To reduce the danger of handling sails away from the safety of the cockpit, roller reefing systems were introduced, such as Ted Hoods"" Jib-Furling Stay, U.S Pat. No. 3,611,969 in 1971. However, the sails made for roller reefing systems are soft, and do not hold their airfoil shape sufficiently.
In accordance with the present invention a stowable wing comprises xe2x80x9cdual semi-rigid sail panelsxe2x80x9d that furl (unfold) or reef (fold down), has an automatic draft (thickness of wing) adjusting boom that bends to the shape of a wing or opens as a spinnaker sail. Wing sail shape is comprised of xe2x80x9csmooth laminated lightweight coredxe2x80x9d sail panels, with shape control springlines, twin booms, and spare sail pockets.
Accordingly, several objects and advantages of the present invention are:
(a) to provide a rigid wing sail for a multitude of different wind powered craft.
(b) to provide a rigid wing sail that is one hundred percent efficient in its use of the winds power.
(c) to provide a rigid wing sail that folds up or down to a desired setting.
(d) to provide a rigid wing sail that is flexible enough to bend to a desired shape.
(e) to provide a rigid wing sail that easily adjusts its shape to the optimum setting for deriving the most power from the wind.
(f) to provide a rigid wing sail that stows its spare panels, freeing up space normally taken by spare bags of sails.
(g) to provide a rigid wing sail that automatically adjusts wing chord draft.
(h) to provide a rigid wing sail that automatically sets as a wing sail or spinnaker sail to the direction of the wind.
(i) to provide a rigid wing sail that is lightweight enough to replace existing sail systems.
(j) to provide a rigid wing sail system that is lower in cost than other standard sail systems"" entire suits of sails.
(k) to provide a rigid wing sail that is safer for everyday use.
(l) to provide a rigid wing sail that as a single system, can be used as a source of power for sailing craft, in all but the most intolerable wind strengths.
(m) to provide a rigid wing sail that has a higher lift to drag ratio for sailing closer upwind.
(n) to provide a rigid wing sail that balances the sail across the mast for easier operation, and less strain on the sail handling gear.
(o) to provide a rigid wing sail with a center of effort that is placed forward to be compatible with existing mast locations of sailing craft.
Further objects and advantages are to provide a rigid wing sail that with its improved efficiency has a lowered designed height, which lowers the centers of both effort and gravity. Thereby, providing the wind powered craft with a higher righting moment. Additionally, causing less heeling of the craft, which further improves efficiency by standing the sail up for less airflow to spill off. Still further objects and advantages will become apparent from a consideration of the ensuing description and drawings.